The present invention relates to a composition which comprises a block copolymer having fluorinated monomer units and to the use of said block copolymer as substrate wetting, anti-cratering and/or leveling agent for coating, ink and/or adhesive compositions.
Smooth and crater free surfaces are important for almost all coating, ink and adhesive applications; they provide not only a visually appealing film but serve also as a protective barrier for the substrate as well as homogenous bond strength throughout the film.
When e.g. the coating is not homogenous and some parts of the surface are only thinly, or not all, coated it leads to poor protection of the substrate. As a result, substrate wetting, anti cratering and leveling agents are added to all sorts of coatings. These difficulties in application of coaling resin, particularly in liquid systems, occur particularly when the surface tension of the liquid system is high and the surface tension of the substrate, or contaminants on the substrate, is much lower. The addition of substrate wetting and anti cratering additives reduces both the dynamic and static surface tension of the liquid coating, leading to smoother film formation.
As long as the viscosity of the coating formulation is low, sufficient substrate wetting and leveling can be achieved with commercially available additives. Large problems can be observed in the cases of high solids coatings, powdered coatings and high speed coating processes. There is a strong demand for substrate wetting and anti-cratering additives with a very low dynamic surface tension, which can provide smooth and uniform films in these highly demanding applications.
The same reasoning applies also for inks and adhesives.
Long chain perfluoro chemicals, typically with perfluorinated chains of length C8 and longer, are used as anti-cratering and leveling agents for coating compositions but are know to form very environmentally persistent degradation products, including perfluoro-octanoic acid (PFOA). Thus, there is a need for alternatives which do not form such environmentally persistent degradation products. However, any improvement in degradation properties should not be achieved at the expense of properties which are relevant for leveling agent such as low dynamic surface tension. In general, the effect on dynamic surface tension reduction is believed to decrease with the order of the perfluorinated unit.
WO 2005/059048 describes coating compositions containing leveling agents prepared by nitroxide mediated polymerization. Monomer units may be substituted by fluoro or perfluoro.
WO 2009/103613 describes the use of short perfluorinated chains in copolymers prepared by nitroxide mediated polymerization for the use of leveling agents.